Solenoid Valve, in Particular, a Pressure Control Valve

ABSTRACT

A solenoid valve has a housing having work, pressure, and tank connectors. An armature is movably arranged in the housing and cooperates with a coil. A slide is moveably arranged in the housing and has a hydraulic chamber connected to the work connector and connectable to the pressure connector. A plunger is positioned between the armature and the slide. The armature acts on the plunger which acts on the slide for moving the slide against a counter force. The plunger has a cross-section and the slide has a piston surface cooperating with the plunger, wherein the cross-section is smaller than the piston surface. In another embodiment, the slide has a first end, loaded by a supply pressure of the pressure connector, and a second end, loaded by a return pressure, so that the slide is hydraulically tensioned by the supply pressure and the return pressure.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a divisional of allowed U.S. patentapplication Ser. No. 09/921,292 filed Aug. 2, 2001.

BACKGROUND OF INVENTION

[0002] 1. Field of the Invention

[0003] The invention relates to a solenoid valve, in particular, apressure control valve, comprising an armature with which by means of aplunger the slide is movable against a counter force, or comprising anarmature and a slide which can be moved against a counter force.

[0004] 2. Description of the Related Art

[0005] In a known solenoid valve a plunger is fastened in the armatureand forms the closing element of the valve in order to control the flowfrom a pressure connector connected to a pressure medium source to aconnector which is connected to a tank or the low-pressure chamber. Thearmature separates two armature chambers from one another which areconnected with one another by a channel which extends through thearmature and the plunger. This prevents the deposition of dirt particleswhich could impair the function of the solenoid valve.

SUMMARY OF INVENTION

[0006] It is an object of the present invention to configure thesolenoid valve of the aforementioned kind such that an optimal functionof the valve is ensured.

[0007] In accordance with the present invention, this is achieved inthat the plunger has a smaller cross-section than the piston surface ofthe slide cooperating therewith, wherein the slide has at least onehydraulic chamber which is connected with at least one work connectorand is connectable with a pressure connector. According to anotherembodiment, this object is achieved in accordance with the presentinvention in that the slide is hydraulically suspended or tensioned bybeing loaded from one end by the supply pressure and from the other endby the return pressure.

[0008] With the first embodiment of the solenoid valve according to thepresent invention it is possible to control large cross-sectionalsurfaces on the slide with relatively small solenoids without requiringa pilot control with control oil loss. The hydraulic chamber of theslide is connected with the work connector. When the solenoid valve issupplied with current, the slide is moved by means of the armature andthe plunger such that the work connector is connected with the pressureconnector. The solenoid valve according to the invention can be usedadvantageously in automatic transmissions or CVT-type (continuouslyvariable transmission) systems.

[0009] In the second embodiment of the solenoid valve according to theinvention, the slide is always hydraulically suspended or pre-tensioned.The supply pressure of the hydraulic medium is applied on one end of theslide, while the slide is loaded on the other end by the returnpressure. In accordance with the pressure difference, the slide is thuscorrespondingly adjusted to the pilot control pressure. The adjustmentof the slide, even in the case of contamination and thus increasedfrictional forces, is optimal. As a result of the pressure reductionbetween the supply pressure and the maximum pilot control pressure, thesolenoid valve according to the invention is optimally stabilizeddespite sufficiently high adjusting forces acting on the slide.

BRIEF DESCRIPTION OF DRAWINGS

[0010]FIG. 1 is a sectional view of the first embodiment of the solenoidvalve according to the invention.

[0011]FIG. 2 is a sectional view of the second embodiment of thesolenoid valve according to the invention.

DETAILED DESCRIPTION

[0012] The solenoid valve according to FIG. 1 has a cup-shaped housing 1in which an armature 2 is moveably arranged. The armature 2 issurrounded by a coil 3 arranged within the housing 1. In a central bore4 of the armature 2 a bushing 5 is fastened which is open at its endfacing the bottom 6 of the housing 1. The bushing 5 projects axiallypast the armature 2 through a bore 7 provided in a magnet yoke 8. Themagnet yoke 8 has a central depression 9 into which the armature 2projects with one end. The opposite end of the armature 2 is providedwith a depression 10 which receives a pressure spring 11. The spring 11is supported with one end on the bottom 12 of the depression 10 and withthe other end on the bottom of a cup-shaped insulation 13. Theinsulation cup 13 separates the armature 2 from the coil 3.

[0013] A seal 14 is positioned on the end of the armature 2 projectinginto the depression 9 of the magnet yoke 8 and surrounds the bushing 5.When the armature 2 is moved, the seal 14 rests sealingly against thebottom 15 of the depression 9 of the magnet yoke 8.

[0014] The magnet yoke 8 is provided at the end face facing away fromthe armature 2 with a depression 16 into which the bushing 5 projects.The end of the bushing 5 positioned in this depression 16 is closed.Adjacent to this end, the bushing 5 is provided with at least onetransverse bore 17 which connects the depression 16 with the interiorchamber or bore 18 of the bushing 5.

[0015] A plunger 19 rests against the end face of the bushing 5. Theplunger 19 can be attached to the end face of the bushing 5. However, itis also possible that the plunger 19 simply rests under the force of thepressure spring 20 against the end face of the bushing 5. The plunger 19is guided in the receiving bore 21 of the housing part 22. The plunger19 has at its circumference an annular groove 23 which is incommunication with a channel 24 that extends through the housing part22. Via this channel 24 the annular groove 23 is connected to theannular chamber 25 which surrounds the housing part 22 and is connectedwith the tank.

[0016] The housing part 22 has a shallow depression 26 at its end facefacing the magnet yoke 8 which communicates by means of a furtherchannel 27 extending through the housing part 22 with the annularchamber 25. The shallow depression 26 and the depression 16 of themagnetic yoke 8 together form a hydraulic armature chamber 16, 26.

[0017] The plunger 19, which is guided so as to be sealed by at leastone annular seal 28 in the receiving bore 21, is connected with a hollowpiston 29. The plunger 19 can simply rest against the hollow piston 29or can be fixedly connected thereto. The hollow piston 29 forms a slidewhich is movably and sealingly guided in a bore 30 of a projection 31 ofthe housing part 22. By means of the projection 31 the solenoid valve isinserted into the bore (not illustrated) of a component, wherein theprojection 31 is seated in a sealed arrangement in the bore by means oftwo annular seals 32, 33 which are spaced axially from one another.

[0018] The end of the slide 29 which is facing away from the plunger 19is engaged by one end of a pressure spring 20; the other end of thespring 20 is supported on a closure element 34 which is inserted intothe projection 31. The closure element 34 is fixedly seated in theprojection 31 and has a central opening 35.

[0019] The hollow piston 29 limits with its piston surface or end face36 facing the plunger 19 a pressure chamber 37. The chamber 37 isdelimited at the opposite end by the bottom 38 of the bore 30. Thepressure chamber 37 is penetrated centrally by the plunger 19 which hasa smaller cross-section than the hollow piston 29 at its end facing theplunger 19. The pressure chamber 37 is connected by at least one axialbore 39 with the interior space 40 of the hollow piston 29 forming ahydraulic chamber (40). At a location spaced from the piston surface orend face 36, the interior space 40 of the hollow piston 29 is connectedwith an annular groove 42 provided on its outer side.

[0020] The housing projection 31 has a radial pressure connector Pwhich, when the solenoid is not excited, is closed by the hollow piston29. When the solenoid is supplied with current, the armature 2 isaxially moved against the force of the pressure spring 20. The armature2 moves the hollow piston 29 by means of the bushing 5 and the plunger19. The annular groove 42 is thus connected with the pressure connectorP so that the pressurized hydraulic medium can flow via the transversebore 41 into the interior space or hydraulic chamber 40 of the hollowpiston 29. From here, the hydraulic medium flows via the opening 35 inthe closure element 34 to the work connector A and thus to thecorresponding consumer.

[0021] The housing chamber 9 is in hydraulic flow communication with anarmature chamber 43 via the bushing 5 and the solenoid armature 2. Thecontrol pressure is present at the work connector A provided at the endface (34). Depending on the position of the hollow piston 29 when thesolenoid is excited, the pressure connector P is opened to a smaller orlarger degree. Within the solenoid area, the tank connector T isprovided which is connected with the annular chamber 25.

[0022] The pressure chamber 37 is loaded with the pressure which ispresent at the work connector A because the pressure chamber 37 isconnected via the bore 39 and the interior space or hydraulic chamber 40of the hollow piston 29 with the work connector A. Accordingly, the endresult is that the control pressure acts only on the surface of theplunger 19 which is then compared with the magnetic force of thesolenoid part 44 of the solenoid valve. The transfer onto thesubstantially greater end face 36 of the hollow piston 29 serves forgenerating an oil volume control through the hollow piston 29. The flowforces acting on the hollow piston 29 are received via the solenoid part44 and the pressure surface by the plunger 19. The solenoid valve isconfigured as a pressure control valve in which the hollow piston 29controls the control pressure at the working connector A by means of thecontrol edges on the pressure connector P or the tank connector T towardthe interior space or hydraulic chamber 40 of the hollow piston 29. Thetwo pressure springs 11, 20 serve for pre-tensioning the hollow piston29 and the armature 2 in order to keep the dead area of thepressure/strength of current characteristic line of the solenoid valveas small as possible.

[0023] The hydraulic pressure which is present at the work connector Ais controlled as a result of the different surfaces of the hollow piston29 and the plunger 19 loaded by the hydraulic medium within the pressurechamber 37 via the surface of the plunger 19. By means of the channel 27the annular chamber 25 is connected with the hydraulic armature chamber16, 26. The annular chamber 25 is in flow communication with the tankvia the tank connector T. The plunger 19 is moreover decoupled betweenin the hydraulic main stage and the main solenoid part 44 by the channel24 which connects the annular channel 23 of the plunger 19 with theannular chamber 25. Accordingly, dirt particles which, coming from themain control area with the hollow piston 29, reach the solenoid area;are returned via this channel 24 into the annular chamber 25 and thus tothe tank (T). The pressure loss at the plunger 19 from the workconnector A toward the solenoid part 44 is thus reduced via this channel24.

[0024] In other respects, the solenoid part 44 of the solenoid valve isproperly encapsulated (sealed) with regard to fluid flow.

[0025] As a result of the described configuration, it is possible tocontrol with relatively small solenoids large cross-sectional surfaceson the hollow piston 29 without providing a true pilot control withcontrol oil losses. The solenoid valve makes possible large controlledquantities without running the risk of contamination. The solenoid valvecan be used preferably in an automatic transmission or CVT-type systems.The solenoid part 44 of the solenoid valve is integrated as the mainstage into the solenoid valve.

[0026] The compensation of the liquid volumes between the two hydraulicarmature chambers 16, 26 and 43 during switching of the solenoid valveis realized in that the hydraulic medium is moved back and forth via thetransverse bore 17 and the interior chamber 18 of the bushing 5. Sincethe interior chamber 18 of the bushing 5 and the adjoining area of thebore 4 within the solenoid armature 2 are relatively long, dirtparticles can be trapped reliably so that they cannot cause a functionaldisruption of the solenoid valve.

[0027] The solenoid valve according to FIG. 2 is a pilot-controlledpressure valve in which the slide 29 is hydraulically suspended orpretensioned by being loaded on both ends. In the illustrated embodimentof FIG. 1, the slide 29 is pretensioned only by the pressure spring 20.In order to achieve the hydraulic tensioning of the slide 29, anauxiliary piston 45 is seated in the end of the slide 29 adjoining theclosure element 34. The auxiliary piston 45 rests under the hydraulicpressure against the closure element 34 and is supported in a sealedfashion within the slide 29. The auxiliary piston 45 delimits theinterior space 40 of the slide 29 which is loaded under the force of thepressure spring 20 in the direction toward the solenoid part 44. Theauxiliary piston 45 has a pressure surface 46 which is smaller than theopposite end face 36 of the slide 29. For example, the pressure surface46 of the auxiliary piston 45 can be only half the size of the end face36. The pressure surface 46, for example, can also be only one third orone fifth of the surface of the end face 36 of the slide 29.Accordingly, the pilot control pressure acting onto the end face 36 ofthe slide 29 can operate also with a correspondingly small supplypressure. This not only contributes to an improved adjustment of theslide 29, for example, when contamination and/or higher frictionalforces occur, but also serves for a higher stabilization as a result ofthe pressure reduction from the pilot control pressure to the supplypressure. This provides a minimal force gain and a higher stability. Theinstability which can be observed in conventionally pilot-controlledpressure control valves as a result of the internal high force gain doesnot occur in this solenoid valve without the adjusting forces which acton the slide 29 becoming so small that the slide could jam. The pressurereduction can occur depending on the surface ratios of the pressuresurface 46 of the auxiliary piston 44 and the pressure surface 36 of theslide 29.

[0028] The solenoid part 44 has a housing 1 which receives the armature2 and the coil 3 surrounding it. The solenoid armature 2 projects intothe depression 9 of the magnet yoke 8. In the central bore 4 the bushing5 is seated which projects through the bore 7 of the solenoid yoke 8. Inthe bushing 5 a plunger 19 in the form of the support pin is providedwhich supports on its end projecting-axially past the bushing 5 aclosing element 47 with which a central opening 48 in the bottom 49 of acup 50 can be closed. The cup 50 limits the pressure chamber 37 which islimited at the other end by the end face 36 of the slide 29. The closingelement 47 is positioned in a hydraulic chamber 51 which is providedbetween the bottom 49 of the cup 50 and the magnet yoke 8 and opens intothe tank connector T.

[0029] The slide 29 has an axial bore 52 which is closed relative to theinterior space 40. In the vicinity of the hydraulic chamber 40 at leastone transverse bore 53 opens into the bore 52, and the bore 52 isconnected by the at least one transverse bore 53 to the pressureconnector P.

[0030] The slide 29 is provided with an annular groove 42 which forms acorresponding annular chamber into which at least one work connector Aopens. The bore 54 provided in the slide 29 opens into the annularchamber 42 and connects the annular chamber 42 with the interior space(hydraulic chamber) 40.

[0031] The bore 52 is provided in the vicinity of the pressure chamber37 with a nozzle-like constriction 55. The pressure chamber 37 is influid communication with the transverse bore 53 via the bore 52.

[0032] The housing part 22 of the solenoid valve is inserted, in thesame way as in the above described embodiment, into a bore (notillustrated) of a component in which the housing part 22 is sealinglyseated by means of three annual seals 32, 33, 56 spaced apart from oneanother in the axial direction.

[0033] In the position illustrated in FIG. 2, the closing element 47rests sealingly on the bottom 49 of the cup 50 and closes the opening48. Accordingly, the pressure chamber 37 is separated from the tankconnector T. The slide 29 is in a central position in which the workconnector A is separated from the pressure connector P and from the tankconnector T in the housing part 22. The slide 29 is alwayspressure-tensioned by the control pressure acting on the end face 36 andthe return pressure acting in the opposite direction onto the pressuresurface 46 of the auxiliary piston 45. The return pressure is assistedby the force of the pressure spring 20 which acts in the same directionas the return pressure. With this pressure tensioning system, anexcellent adjustment of the slide 29 is ensured even when contaminationand thus higher frictional forces are present.

[0034] The two main control edges 57, 58 on the slide 29 control thepressure from the pressure connector P to the work connector A and fromthe work connector A to the tank connector T of the housing part 22.

[0035] As a result of the hydraulic pressure acting on the pressuresurface 46 in the interior space 40, the auxiliary piston 45 is alwaysforced against the closure element 34 which is provided with at leastone opening 60. By means of this opening 60, a hydraulic chamber 61positioned between the slide 29 and the closure element 34 is connectedwith the tank T. Moreover, the hydraulic medium acts on the bottom 59 ofthe interior space 40 so that the slide 29 is loaded in the directiontoward the solenoid part 44. By means of this pressure, the slide 29 isalways adjusted according to the pilot control pressure in the pressurechamber 37.

[0036] The bottom 59 of the interior space or hydraulic chamber 40 ofthe slide 29 has a smaller surface than the oppositely positioned endface 36 of the slide 29.

[0037] The solenoid valve operates normally by pilot control with thesupply pressure P. Via the transverse bore 53 the pressurized hydraulicmedium reaches the axial bore 52 of the slide 29. Via the nozzle 55 thepressurized hydraulic medium reaches the pressure chamber 37. The returncontrol is realized by the closing element 47 of the solenoid part 44.Since a larger force is acting on the end face 36 of the slide 29 thanon the oppositely positioned surface of the bottom 59 of the hydraulicchamber 40 plus the force of the pressure spring 20, the slide 29 ismoved from the position illustrated in FIG. 2 against the force of thepressure spring 20. The control edge 57 opens the pressure connector Pso that the hydraulic medium under pressure can reach via the annularchamber 42 the work connector A. At the same time, the control edge 58closes the connection of the tank connector T to the work connector A.The return of the hydraulic medium is realized via the bore 54 to theend face 46 of the auxiliary piston 45. Accordingly, in the waydescribed above, the slide 29 is always adjusted according to the pilotcontrol pressure within the pressure chamber 37.

[0038] When the solenoid part 44 is actuated, the plunger 19 with theclosing element 47 is moved back so that the opening 48 in the bottom 49of the cup 50 is released. The hydraulic medium in the pressure chamber37 can flow via the opening 48 to the tank connector T. Accordingly, theslide 29, as a result of the pressure drop within the pressure chamber37, is moved in the downward direction (FIG. 2) so that the connectionbetween the pressure connector P and the work connector A is closed andthe connection from the work connector A to the tank connector T isopened. The hydraulic medium can thus flow back to the tank T.

[0039] The slide 29 is pressure-tensioned in any position. The pilotcontrol pressure within the hydraulic chamber 37 acts onto one end face36, while the return pressure acts on the bottom 59 of the interiorspace 40. This serves for an improved adjustment of the slide 29 evenwhen contamination and thus higher frictional forces are present.

[0040] The pressure reduction between the supply pressure P and themaximum pilot control pressure within the pressure chamber 37, whichdepends on the surface ratio of the surface of the bottom 59 and the endface 36 of the slide 29, is an important advantage of the solenoid valveaccording to the invention. The pressure reduction serves forstabilizing the entire valve despite the fact that sufficiently highadjusting forces acting on the slide 29 are provided.

[0041] While specific embodiments of the invention have been shown anddescribed in detail to illustrate the inventive principles, it will beunderstood that the invention may be embodied otherwise withoutdeparting from such principles.

What is claimed is:
 1. A solenoid valve comprising: a housing (1,22).having a work connector (A), a pressure connector (P), and a tankconnector (T); an armature (2) moveably arranged in the housing (1, 22);a coil (3) arranged in the housing (1, 22) and acting on the armature(2); a slide (29) moveably arranged in the housing (1, 22); the slide(29) having a first end, loaded by a supply pressure of the pressureconnector (P), and having a second end, loaded by a return pressure tothe tank connector (T), so as to be hydraulically tensioned by thesupply pressure and the return pressure.
 2. The solenoid valve accordingto claim 1, further comprising an auxiliary piston (45) arranged in theslide (29) and delimiting a hydraulic chamber (40) of the slide (29). 3.The solenoid valve according to claim 2, wherein the auxiliary piston(45) has a pressure surface (46) that is facing the hydraulic chamber(40) and is loaded by the hydraulic pressure in the hydraulic chamber(40), wherein the slide (29) has an end face (36) loaded by the supplypressure, wherein the pressure surface (46) is smaller than the end face(36).
 4. The solenoid according to claim 2, wherein the housing (1, 22)comprises a closure element (34) and wherein the auxiliary piston (45)rests against the closure element (34) under the force of the returnpressure.
 5. The solenoid according to claim 1, wherein the housing (1,22) has a pressure chamber (37) in which a pilot control pressure ispresent, wherein the pressure connector (P) is connected to the pressurechamber (37).
 6. The solenoid according to claim 5, wherein the slide(29) has at least one bore (52) connecting the pressure connector (P)and the pressure chamber (37).
 7. The solenoid according to claim 6,wherein the pressure chamber (37) is configured to be connected to thetank connector (T).
 8. The solenoid according to claim 7, wherein thepressure chamber (37) has at least one opening (48) and wherein thearmature (2) has a closing element (47) configured to controllably closethe opening (48).
 9. The solenoid according to claim 8, wherein thepressure chamber (37) is connected with the tank connector (T) when theat least one opening (48) is open.
 10. The solenoid according to claim6, wherein the slide (29) comprises a nozzle (55) arranged in the atleast one bore (52).